In the search for flexible molecular crystals endowed with porosity, we achieved the fabrication of expandable crystalline prototypal structures, which allow the absorption of gases, without modifying the crystal architecture. The design brings together highly symmetrical tetrahedral elements to construct swellable porous adamantoid frameworks through co-operation of eight surrounding hydrogen bonds mounted on conformationally flexible groups. The flexibility of the porous crystals manifests itself in response to stimuli of selected gases, which promote reversible conformational changes, inducing breathing in the molecular structure. The backbone of the reticular construction is based on the formation of the carboxylic dimers, which project outwards from the tetrahedral molecular core to consolidate the 3D framework. Contact with proper gases such as CO2, Xe and hexane triggers a 56-70% enlargement of the channel cross-section. The accommodation of CO2 and Xe in the channel chambers was revealed by synchrotron-light X-ray diffraction, combined with molecular dynamics and density functional theory (DFT) theoretical calculations. Rare experimental observations of xenon dynamics, in which Xe diffuses along the channels and experiences different chamber orientations in the crystal, were gathered by analysing 129Xe NMR chemical shift anisotropy profiles, which encode the shape and orientation of each visited cavity along the channel. The jump rate and activation energy experienced was uniquely established by exploring Xe atoms in their diffusional path. Nitrogen showed a low affinity to the matrix and was unable to enlarge the pores, thus it was excluded from the restrictive pores of the empty crystal. Given the properties of molecular crystals, it is possible to outline some advantageous aspects, such as simple design, easy self-assembly, solubility, reversible gas uptake and absence of metal ions, and they can thus be considered for eco-friendly gas capture and separation.

Bassanetti, I., Bracco, S., Comotti, A., Negroni, M., Bezuidenhout, C., Canossa, S., et al. (2018). Flexible porous molecular materials responsive to CO2, CH4 and Xe stimuli. JOURNAL OF MATERIALS CHEMISTRY. A, 6(29), 14231-14239 [10.1039/c8ta02211a].

Flexible porous molecular materials responsive to CO2, CH4 and Xe stimuli

Bassanetti, Irene
Primo
Membro del Collaboration Group
;
Bracco, Silvia
Secondo
Membro del Collaboration Group
;
Comotti, Angiolina
Membro del Collaboration Group
;
Negroni, Mattia
Membro del Collaboration Group
;
Bezuidenhout, Charl
Membro del Collaboration Group
;
Sozzani, Piero
Ultimo
Membro del Collaboration Group
2018

Abstract

In the search for flexible molecular crystals endowed with porosity, we achieved the fabrication of expandable crystalline prototypal structures, which allow the absorption of gases, without modifying the crystal architecture. The design brings together highly symmetrical tetrahedral elements to construct swellable porous adamantoid frameworks through co-operation of eight surrounding hydrogen bonds mounted on conformationally flexible groups. The flexibility of the porous crystals manifests itself in response to stimuli of selected gases, which promote reversible conformational changes, inducing breathing in the molecular structure. The backbone of the reticular construction is based on the formation of the carboxylic dimers, which project outwards from the tetrahedral molecular core to consolidate the 3D framework. Contact with proper gases such as CO2, Xe and hexane triggers a 56-70% enlargement of the channel cross-section. The accommodation of CO2 and Xe in the channel chambers was revealed by synchrotron-light X-ray diffraction, combined with molecular dynamics and density functional theory (DFT) theoretical calculations. Rare experimental observations of xenon dynamics, in which Xe diffuses along the channels and experiences different chamber orientations in the crystal, were gathered by analysing 129Xe NMR chemical shift anisotropy profiles, which encode the shape and orientation of each visited cavity along the channel. The jump rate and activation energy experienced was uniquely established by exploring Xe atoms in their diffusional path. Nitrogen showed a low affinity to the matrix and was unable to enlarge the pores, thus it was excluded from the restrictive pores of the empty crystal. Given the properties of molecular crystals, it is possible to outline some advantageous aspects, such as simple design, easy self-assembly, solubility, reversible gas uptake and absence of metal ions, and they can thus be considered for eco-friendly gas capture and separation.
Articolo in rivista - Articolo scientifico
hydrogen bonds; molecular crystals; flexible porous materials; solid state NMR of CO2, Xe NMR
English
22-giu-2018
2018
6
29
14231
14239
partially_open
Bassanetti, I., Bracco, S., Comotti, A., Negroni, M., Bezuidenhout, C., Canossa, S., et al. (2018). Flexible porous molecular materials responsive to CO2, CH4 and Xe stimuli. JOURNAL OF MATERIALS CHEMISTRY. A, 6(29), 14231-14239 [10.1039/c8ta02211a].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/218832
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